Conventionally, MEMS switch has been known as a microscopic electromechanical component for turning on and off electrical signals. For example, the MEMS switch disclosed in Japanese Patent Laid-Open No. H9-17300 is fabricated over a substrate by a fine structure fabrication technique for use in the fabrication of semiconductor devices. A projection, which functions as an anchor (support), of an insulator is formed over a substrate, and a beam of an insulating film is fixed on the anchor. An upper electrode is formed at the upper part of the beam, and a contact portion facing downward is formed at the tip of the beam. A lower electrode is formed over the substrate opposite to the upper electrode, and a signal line is formed over the substrate under the contact portion.
When voltage is not applied to the upper or lower electrode, the contact portion and the signal line are away from each other, and the switch is off. When voltage is applied, the beam is elastically deformed by Coulomb force exerted between the upper electrode and the lower electrode, and is warped toward the substrate. As a result, the contact portion is brought into contact with the signal line, and the switch is thereby turned on.
In mobile telephones and the like, a battery is used as power supply, and thus switch operation must be performed on 3V or so. To lower the operating voltage, the restoring force of springs must be reduced. However, when the restoring force is weakened as mentioned above, the upper electrode and the lower electrode or the contact portion and the signal line do not separate from each other due to sticking phenomenon. As a result, the operating voltage becomes difficult to lower.
An example of methods for solving this problem is disclosed in Japanese Patent Laid-Open No. 2002-326197. This method is such that a projection is formed at some point on a spring and thereby the restoring force is increased when a sticking phenomenon takes place.